1. Field of the Invention
This invention relates in general to high definition television (HDTV) digital video content protected systems, and more particularly to the transmission of High-Bandwidth Digital Content Protection (HDCP) control data over a single communication channel.
2. Background of the Invention
With an advent of high-definition digital video data there is a need to prevent copying and redistribution of the digital content. HDCP specification was developed to protect digital entertainment content across the Digital Video Interface (DVI)/High-Definition Multimedia Interface (HDMI) high-definition digital video delivery systems. The HDCP specification provides a robust, cost-effective and transparent method for transmitting and receiving digital entertainment content to DVI/HDMI-compliant digital displays.
Referring now to FIG. 1, a conventional HDCP-protected system for transmitting high definition audio and video data is shown. System 100 includes an HDCP transmitter 110 and HDCP receiver 120. The HDCP transmitter 110 is, for example, a High-Definition (HD) capable DVD player, a set-top box, or any other device capable of transmitting HDCP enabled digital content. HDCP receiver 120 is, for example, a HD-capable and HDCP enabled digital display unit, such as a monitor, projector, etc. HDCP transmitter 110 and HDCP receiver 120 are connected via a high speed DVI or HDMI link 170. Link 170 has multiple high-speed differential pairs of transmission lines, such as signal lines 150a, 150b, and 150c that carry high-speed digital video data. Signal lines 150a, 150b, and 150c are Transition Minimized Differential Signaling (TMDS) lines, which carry 24 bits of digital video data. For example, 150a transmits 8 bits that are used for a red channel, 150b transmits 8 bits that are used for a green channel, and 150c transmits 8 bits that are used for a blue channel. Signal line 150d transmits a TMDS clock signal.
Link 170 also has two low-speed signal lines 130 and 140 that are used by the HDCP transmitter 110 and HDCP receiver 120 to exchange HDCP control information. As per the HDCP V1.1 specification developed by Digital Content Protection LLC, all HDCP control data flowing between the HDCP transmitter 110 and HDCP receiver 120 are communicated over the I2C bus serial interface (I2C_V2.1) of the HDCP-protected interface. I2C bus is a two-wire serial bus. The two I2C signals are serial data (SDA) and serial clock (SCL) signals. Signal line 130 is a signal line for transmitting serial clock signal (SCL). Signal line 140 is an SDA bi-directional signal line for transmitting data, such as HDCP related control data and addresses of the HDCP receiving device, between HDCP transmitter 110 and HDCP receiver 120.
All HDCP authorized devices, such as HDCP transmitter 110 and HDCP receiver 120 are given a set of unique secret device keys from the Digital Content Protection LLC. The secret keys consist of an array of forty 56-bit secret device keys and a corresponding 40-bit binary Key Selection Vector (KSV). HDCP transmitter 110 initiates authentication by sending an initiation message that includes its Key Selection Vector, AKSV, and a 64-bit value An. HDCP receiver 120 responds by sending a message containing its Key Selection Vector, BKSV. HDCP transmitter 110 confirms that the received KSV has not been revoked. At this point, both HDCP transmitter 110 and HDCP receiver 120 calculate a shared value, which will be equal, if both devices 110 and 120 have a set of valid keys. Authentication has now been established.
During initialization and periodically after initialization (approximately every 2 seconds) of the HDCP operation, HDCP transmitter 110 uses the SCL signal line 130 and SDA signal line 140 to exchange HDCP control information with HDCP receiver 120. The HDCP control data includes HDCP receiver 120 capability (Bcaps), the key selection vectors (Aksv and BKsv), 64-bit values An and Bn, and response values R0 and R0′. The HDCP control data enables both HDCP transmitter 110 and HDCP receiver 120 to check each other's authentication status and properly encrypt and decrypt the high-definition digital video and audio data.
When HDCP transmitter 110 initiates an HDCP data read/write operation, it drives SCL signal line 130 as a clock to synchronize the operation between HDCP transmitter 110 and HDCP receiver 120. During each SCL clock period, SDA 140 signal line carries one bit of control data either from HDCP transmitter 110 or from HDCP receiver 120.
With the introduction and advancement of wireless or fiber based digital video delivery systems, it is desirable to carry HDCP control data using a wireless channel or other single communication channel. However, the existing schemes for transferring HDCP control data cannot be used to transmit control data over a single communication channel. First, the existing schemes use two signal lines for transmitting HDCP control data. One signal line carries an SCL clock signal (such as signal line 130 in FIG. 1). The other signal line carries HDCP control data (for example, signal line 140 in FIG. 1). However, in a wireless network or single communication channel network, a single communication channel is not capable of carrying the two signals at the same time.
In addition, in the wired communication media, the wires are bidirectional, and direction of data transfer can be switched during each clock period. However, in a wireless or fiber based network, direction of data could not be switched from one clock period to another. Hence, it is not feasible to carry the HDCP control related data over a wireless communication channel using known techniques.
It is, therefore, desirable to develop a new implementation scheme to handle transmission of HDCP control data over a single communication channel.